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The /t/ is optionally silent when it follows /n/ and precedes a vowel sound, /r/ (including all r-controlled vowels) or a syllabic /l/.
do you native speakers say "don't ask" as
I am a native speaker of a very general General American and I would say /doʊnʔæsk/ in all cases regardless of formality of speech (I always glottalize /t/ syllable-finally). I might not even understand /doʊnæsk/ if the context didn't make it clear, and certainly it sounds excessively colloquial to me. I never omit /t/ after a nasal; "banter" will have the strong aspirated /t/ even in casual speech. You can't go wrong by pronouncing the t.
I think this is an accent thing.
I'm also Australian, and notice many people drop the "t" in this situation.
However, interestingly it seems to only be after _on't words, and not _an't words.
For example, "don't ask" becomes "doun ask", "won't ask" becomes "woun ask", but "can't ask" becomes "carnt ask" - I suppose because can is the opposite of can't - so silence on the t would lead to confusion.
Though I have heard "carn ask"...again due to accent.
doesn't...this is another one that depends on accent. I've often heard it pronounced as "dozen".
Australian English is a lot more slurred and relaxed than England English though, and will differ from state to state.
In Tasmania, people often sound half asleep ;)
"Howz yuz goinn darl" (meaning how are you going darling) and "howz arz ya" (how are you) is a common greeting that I used to cringe at when I moved to Tasmania!
It is common here for complete strangers to call each other "Darl" (meaning darling) but never heard this in other states of Australia.